With the globalization of business, industry and trade wherein transactions and activities within these fields have been changing from localized organizations to diverse transactions over the face of the world, the telecommunication industries have been expanding rapidly. Wireless telephones and, particularly, cellular telephones have become so pervasive that their world wide number is in the order of hundreds of millions. While the embodiment to be subsequently described relates to cellular telephones, the principles of the invention would be applicable to any wireless personal communication device that could be used to communicate in a cellular telecommunications system. These would include the wide variety of currently available communicating personal palm devices or Personal Digital Assistants (PDAs), which include, for example, Microsoft's WinCE line; the PalmPilot line produced by 3Com Corp.; and International Business Machine Corporation's WorkPad. These devices are comprehensively described in the text, Palm III & PalmPilot, Jeff Carlson, Peachpit Press, 1998. Thus, when the term, wireless telephone is used herein, it is meant to include such devices.
Despite the large numbers of cellular telephones currently in use, the global geographical areas within which cellular telephones may effectively be used remains quite limited. In order to be effectively used the cellular phone must be in range of a cellular array area base tower. While such cellular arrays are present in high population density areas, there is no economic justification to extend such cellular arrays to great portions of United States having low population densities. However, since our society is becoming more global and mobile, a great deal of business and personal activity does take place in these low population density areas and the industry is seeking ways to extend cellular telephone service to such sparse population areas.
In order to better understand the nature of this challenge, the principal forms of telecommunication should be briefly considered. The standard wired telecommunications system, which has been in use world wide for well over 100 years, is the conventional handheld or speaker input wired into a base that in turn is wired into a Public Switched Telephone Network (PSTN) with wired switched channel paths to and from other telephones or like devices through their bases. These telephones are respectively connected to the PSTN via local switching centers or switching nodes in a fully wired telecommunication system. Conventionally these switching centers have many telephones connected to each. The centers operate to control the channel connections, i.e. switch into and out of the PSTN, those calls originated or terminated at telephone stations.
In addition, there have been developed, over the past 20 years, two major mobile wireless systems: 1) the short range wireless radio frequency (RF) “cordless” telephone system; and 2) the mobile wireless long range RF “wireless” telephone system that has been commercialized primarily as the “cellular” telephone system.
The cordless telephone is basically a combination telephone and RF receiver/transmitter. The cordless phone has a base and a handset. The base is wired through any standard phone jack into the conventional PSTN. The base receives the incoming call as a normal phone line signal, converts the signal into an FM RF signal (preferably digital in present technology) and broadcasts the signal over a short range to the mobile handset that receives the signal and converts it into the analog signal that is heard over the phone. When the user speaks, the handset converts the analog speech signal into an FM RF digital signal that is broadcast back to the base that in turn receives and converts the signal back into the line signal to the PSTN. Thus, the cordless telephone base looks like and operates like a conventional wired phone base as far as the PSTN is concerned. The one thing that the cellular long range communication system has in common with the short range cordless system is that both eventually have a base station that looks and acts like a standard wired telephone base with respect to the PSTN.
Before the cellular wireless phone system was developed, long range mobile wireless phones were relatively rudimentary; they were usually in automobiles. There was usually one central tower with about 25 channels available on the tower. The mobile wireless telephone needed a large powerful transmitter, usually in the automobile that had to transmit up to 50 miles. This was too cumbersome for any personal or portable phone. In the cellular system for the handheld mobile wireless phone, an area such as a city is broken up into small area cells. Each cell is about 10 square miles in area. Each has its base station that has a tower for receiving/transmitting and a base connected into PSTN. Even though a typical carrier is allotted about 800 frequency channels, the creation of the cells permit extensive frequency reuse so that tens of thousands of people in the city can be using their cell phones simultaneously. Cell phone systems are now preferably digital with each cell having over 160 available channels for assignment to users. In a large city there may be hundreds of cells, each with its tower and base station. Because of the number of towers and users per carrier, each carrier has a Mobile Telephone Switching Office (MTSO) that controls all of the base stations in the city or region and controls all of the connections to the land based PSTN. When a client cell phone gets an incoming call, MTSO tries to locate what cell the client mobile phone is in. The MTSO then assigns a frequency pair for the call to the cell phone. The MTSO then communicates with the client over a control channel to tell the client or user what frequency channels to use. Once the user phone and its respective cell tower are connected, the call is on between the cell phone and tower via two-way long range RF communication. In the United States, cell phones are assigned frequencies in the 824–894 MHz ranges. Since transmissions between the cell telephone and cell tower are digital, but the speaker and microphone in the telephone are analog, the cell telephone has to have a D to A converter from the input to the phone speaker, and an A to D converter from the microphone to the output to the cell tower.
Although cellular arrays offer a very effective means of wireless communications within their array areas in the order of 10 square miles each, the challenge is extend the cellular array ranges beyond the limits of the array areas.